1. Field of the Invention
The present invention relates to the forming of superimposed patterns on a substrate in the manufacturing of semiconductor devices and the like. More particularly, the present invention relates to a substrate inscribed with alignment marks for ensuring that an upper pattern is formed in alignment with a lower pattern on the substrate. The present invention also relates to a method of forming such alignment marks and to a method of obtaining alignment information for use in superimposing patterns on a substrate, in the manufacturing of a semiconductor device.
2. Description of the Related Art
In general, a semiconductor device is manufactured by forming patterns on a semiconductor substrate. Each pattern is formed through a series of processes. The processes are performed selectively and repeatedly to form the patterns one above the other on the substrate. In this respect, it is very important for a lower pattern (formed by a first series of processes) and an upper pattern (formed by a subsequent series of processes) to be aligned with each other. To this end, alignment marks are used. The alignment marks are formed on a scribe line of the semiconductor substrate which demarcates regions (dies) in which circuit structures are formed
Referring to FIGS. 1 and 2, conventional alignment marks 10 include a main alignment mark 11 in the form of a rectangular band, and a sub-alignment mark 12 disposed at a central region of the main alignment mark 11. The main alignment mark 11 is part of a conductive pattern. The sub-alignment mark 12 is part of a photoresist pattern.
That is, the main alignment mark 11 is formed by a sputtering process in a first series of processes aimed at forming a lower conductive pattern on the semiconductor substrate. The sub-alignment mark 12 is formed by a photolithographic process in a subsequent series of processes aimed at forming an upper pattern on the semiconductor substrate. Distances between the main alignment mark 11 and the sub-alignment mark 12 are measured in lengthwise and widthwise directions of the scribe line. The degree to which the upper pattern and the lower pattern are aligned is determined based on these overlay measurements. Moreover, the overlay measurements are fed back to the processing equipment for use in adjusting the equipment, if necessary, to ensure that subsequently formed patterns are accurately aligned with the previously formed patterns.
However, as shown in FIGS. 1 and 2, the sputtering process may form a protrusion 13 at an inner side of the main alignment mark 11. In this case, a first distance d1 between one inner side of the main alignment mark 11 and an adjacent outer side of the sub-alignment mark 12 is different from a second distance d2 between the other inner side of the main alignment mark 11 and the adjacent outer side of the sub-alignment mark 12. That is, results of the overlay measurements (alignment information) will indicate a difference between the first distance d1 and the second distance d2 even though the sub-alignment mark 12 was centered relative to the main alignment mark 11. Therefore, the results of the overlay measurements will incorrectly indicate that the sub-alignment mark 12 was formed as offset relative to the main alignment mark 11, i.e., that the upper pattern and the lower pattern are misaligned. As a result, the data fed back to the processing equipment as a result of the overlay measurement process will cause the equipment to form a subsequent pattern out of alignment.